The present invention relates to a method for the continuous marking of elongated stock which is moved predominantly in the direction of the physical extension of that stock, that is, the longitudinal extension; and more particularly, the invention relates to markings on the surface of such moving elongated stock, the markings having limited axial extensions and being produced under utilization of one or more dye-jets. The dye is forced in each instance under pressure to emerge from a nozzle which oscillates; the dye-jet is oriented to impinge upon the stock at right angles or at least approximate right angles, to the direction of the stock. Equipment of this kind and to which the invention generally pertains is shown, for example, in German printed Patent Application 1,415,791.
In order to establish the scope of the invention, the term "elongated stock" is used as a general denotation referring, for example, to cores of metallic conductors with or without insulation on top; also included are light-wave conductors and fiber optic conductors in the communications industry. But the term `elongated stock` is not limited to cable and conductors of light and electricity, but also includes hoses or tubes for the conduction of liquid or fluid or electricity. Also included are bundles of any of the foregoing with or without jacket. Core strands of that kind being made for some purpose in a continuous fashion may require for some reason or another some kind of identification. For example individual conductors in a large bundle in which the individual conductors are twisted or stranded require individual identification.
In order to provide an adequate description of the invention, the rather cumbersome term "elongated stock" is avoided and the term "core" or "core strand" is used instead with the understanding that this is just an example of elongated stock and is in that respect simply representative of the more general term "elongated stock". Cores or core strands are, for example, used in communication cables wherein identification and marking is necessary in order to establish a clear identification of individual core elements or cores among a large plurality of physically similar cores, but being bundled, intertwined, and so forth, so that any indentification without marking is difficult or even impossible. Therefore, individual cores in a bundle require identification and it is part of the invention to establish adequate provisions for that purpose. In a more or less simple fashion and by way of example, four cores are stranded together and three of them carry, for example, one, two and three colored bands respectively on their insulation these bands are organized in groups, and it really is the grouping pattern that identifies the three core strands, the fourth core being free, bearing no identifying band. The markings of cores may be established differently in that one of these cores carries bands or rings in a spaced apart relation; another one of the cores carries two bands close together and then there is a space followed by another group of two bands and so forth. The third core may also carry such twin rings but they are as a group spaced farther away than the twin rings of the second core just referred to and the forth core has no rings.
Another way of providing distinctive identification is to use single spaced apart bands but of different colors. It is clear that the way individual cores are identified can be varied to a great degree, but it is also clear that all of these markings require methods whereby the bands so provided firmly adhere to the surface of the cores and remain in place and recognizable even if the core is handled roughly, abrasively, or the like, because for example, stranding, winding, and unwinding, looping or other ways of handing the core require some surface gripping and engagement which inherently involve the possibility that any marking that does not firmly adhere to the surface is simply scratched or wiped away.
German Printed Patent Application 1,415,791 describes equipment for marking cores; the marking equipment is positioned immediately downstream from the extruder by means of which insulating material is deposited on a metallic conductor and within the terminology chosen here the metallic conductor with insulation is a core or core strand. The marking equipment includes a nozzle ejecting a dye-jet which will hit the still rather hot surface of the freshly-extruded insulating material. Owing to the fact that the insulation is still very hot, the dye marking will to some extent diffuse into the soft insulation (and that is highly desirable) and then will dry very quickly. Thus the dye will combine intimately with the insulating material of the core. This renders the dye abrasion-proof to a high degree.
A cooling path is provided downstream from the extruding and marking equipment. This cooling path serves additionally for drying the dye. The method as described in this prior art application is very advantageous in practice. Further improvements include equipment for oscillating the nozzle which ejects the dye-jet. All these pieces of equipment, including the driving aggregates for the oscillation as well as dye containers, are arranged in the immediate vicinity of the dye-jet-emitting head and are, moreover, positioned very close to the extrusion head by means of which insulation is provided on the conductor as stated. The dye-jet should impinge upon the core at right angles. Consequently the nozzle and its ejecting path, oscillating about an axis parallel to the core strand movement, is arranged at right angles to that axis.
The oscillating system of the prior art structure for but actually including the nozzle itself, however, was found to be rather large, bulky and heavy. Contributing to the largeness is the drive for the nozzle. It was found that these large dimensions of the nozzle-plus-drive system are troublesome because one may need two or more nozzles with oscillating systems if, for example, different colors are to be applied to the marking bands. Since, however, the insulating material of the core cools rapidly, the quality and adhesion of the sprayed-on markings deteriorates rapidly with distance from the extruder. In other words, if for example, three different colors are used, that is, if three different dyes have to be emitted from three different dye-spray (equipments) nozzles, one of them is necessarily positioned relatively far from the extruder, while one of them is fairly close. This means that the dye applied to the insulation fairly close to the extruder will adhere quite well to the insulation, but the dye applied by the spraying equipment farthest from the extruder will in fact have limited adhesability. Moreover, if for example, in a continuous manufacturing facility the markings are to be changed for one reason or another, the manufacturing actually has to be interrupted and the existing dye applying equipment or nozzles are exchanged for others, or the containers are exchanged to apply dyes of a different color, and any of these methods may be needed depending on the sophistication and differentiation of marking. Any such equipment change is of course a time consuming procedure and as far as core-cable-stock manufacture is concerned, it simply constitutes down time in which nothing is being produced.